U.S. patent number 4,268,582 [Application Number 06/016,902] was granted by the patent office on 1981-05-19 for boride coated cemented carbide.
This patent grant is currently assigned to General Electric Company. Invention is credited to Thomas E. Hale, Roy C. Lueth.
United States Patent |
4,268,582 |
Hale , et al. |
May 19, 1981 |
**Please see images for:
( Certificate of Correction ) ** |
Boride coated cemented carbide
Abstract
A coated cemented carbide article comprises a cemented carbide
substrate, the surface regions thereof having diffused therein an
element such as boron, silicon or aluminum. The article further
comprises a coating disposed on the diffused substrate, the coating
being a boride such as titanium boride, hafnium boride, zirconium
boride or tantalum boride. In another embodiment the coated
cemented article further includes an interlayer sandwiched between
the diffused substrate and the boride coating, the interlayer being
one or more layers formed from the carbides, nitrides or
carbonitrides of elements from groups IVb and Vb of the Periodic
Table of Elements, and combinations thereof.
Inventors: |
Hale; Thomas E. (Warren,
MI), Lueth; Roy C. (Marine City, MI) |
Assignee: |
General Electric Company
(Detroit, MI)
|
Family
ID: |
21779627 |
Appl.
No.: |
06/016,902 |
Filed: |
March 2, 1979 |
Current U.S.
Class: |
428/552; 419/12;
427/249.15; 427/249.5; 427/419.7; 428/446; 428/472; 428/627;
428/698; 428/911; 428/932; 428/938; 75/238 |
Current CPC
Class: |
B23B
27/148 (20130101); C23C 16/38 (20130101); C23C
30/005 (20130101); Y10S 428/932 (20130101); Y10T
428/12576 (20150115); Y10S 428/938 (20130101); Y10S
428/911 (20130101); Y10T 428/12056 (20150115) |
Current International
Class: |
B23B
27/14 (20060101); C23C 16/38 (20060101); C23C
30/00 (20060101); C23C 011/14 (); B32B 013/04 ();
B32B 031/24 () |
Field of
Search: |
;428/446,472,911,539,627,932,938 ;427/249,419F,419.7
;75/202,203,205,238 ;148/6,6.3,31,31.5 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Ansher; Harold
Attorney, Agent or Firm: Morgan,Finnegan, Pine, Foley &
Lee
Claims
What is claimed is:
1. A coated cemented carbide article comprising: a cemented carbide
substrate, the surface region of said substrate having diffused
therein for predetermined a depth an element selected from the
group consisting of boron, silicon, and aluminum; and a coating
disposed on said diffused substrate surface said coating being a
boride selected from the group consisting of titanium boride,
hafnium boride, zirconium boride, and tantalum boride.
2. A coated cemented carbide article as recited in claim 1 in which
the element diffused into the surface region of the cemented
carbide substrate is boron.
3. A coated cemented carbide article as recited in claim 1 in which
the element diffused into the surface region of the cemented
carbide substrate is silicon.
4. A coated cemented carbide article as recited in claim 1 in which
the element diffused into the surface region of the cemented
carbide substrate is aluminum.
5. A coated cemented carbide article as recited in claim 1 wherein
said cemented carbide substrate has a cobalt content greater than
10% by weight.
6. A coated cemented carbide article as recited in claim 5 in which
said boride coating is titanium boride.
7. A coated cemented carbide article as recited in claim 5 in which
said boride coating is hafnium boride.
8. A coated cemented carbide article as recited in claim 5 in which
said boride coating is zirconium boride.
9. A coated cemented carbide article as recited in claim 5 in which
said boride coating is tantalum boride.
10. A coated cemented carbide article having a cobalt content
greater than 10% by weight comprising:
a cemented carbide substrate, the surface region of said substrate
having diffused therein boron for a predetermined depth; and a
titanium boride coating disposed on said boron diffused
substrate.
11. A coated cemented carbide article comprising:
a cemented carbide substrate;
an interlayer disposed on said substrate, said interlayer including
at least one layer selected from the group consisting of the
carbides, nitrides and carbonitrides of elements from groups IVb
and Vb of the Periodic Table of Elements, and combinations of said
carbides, nitrides and carbonitrides of elements from groups IVb
and Vb of the Periodic Table of Elements; and
a coating disposed on said interlayer said coating being a boride
selected from the group consisting of titanium boride, hafnium
boride, zirconium boride and tantalum boride.
12. A coated cemented carbide article as recited in claim 11 in
which the coating is titanium boride.
13. A coated cemented carbide article as recited in claim 11 in
which the coating is hafnium boride.
14. A coated cemented carbide article as recited in claim 11 in
which the coating is zirconium boride.
15. A coated cemented carbide article as recited in claim 11 in
which the coating is tantalum boride.
16. A coated cemented carbide article as recited in claim 11 in
which the surface region of the substrate, upon which is disposed
said interlayer, is diffused with an element selected from the
group consisting of boron, silicon and aluminum.
17. A coated cemented carbide article as recited in claim 16 in
which the element diffused into said surface region of the
substrate is boron.
18. A coated cemented carbide article as recited in claim 16 in
which the element diffused into said surface region of the
substrate is silicon.
19. A coated cemented carbide article as recited in claim 16 in
which the element diffused into said surface region of the
substrate is aluminum.
20. A coated cemented carbide article comprising:
a cemented carbide substrate, the surface region of said substrate
having diffused therein an element selected from group consisting
of boron, silicon and aluminum;
an interlayer disposed on said diffused surface region of the
substrate, said interlayer including at least one layer selected
from the group consisting of the carbides, nitrides, carbonitrides
of elements from groups IVb and Vb of the Periodic Table of
Elements, and combinations of said carbides, nitrides and
carbonitrides of elements from groups IVb and Vb of the Periodic
Table of Elements; and
a coating disposed on said interlayer, said coating being a boride
selected from the group consisting of titanium boride, hafnium
boride, zirconium boride and tantalum boride.
21. A coated cemented carbide article comprising:
a cemented carbide substrate, the surface region of said substrate
having boron diffused therein a predetermined depth;
an interlayer disposed on said boron diffused substrate, said
interlayer including at least one layer selected from the group
consisting of the carbides, nitrides and carbonitrides of elements
from groups IVb and Vb of the Periodic Table of Elements, and
combinations of said carbides, nitrides and carbonitrides of
elements from groups IVb and Vb of the Periodic Table of Elements;
and
a titanium boride coating disposed on said interlayer.
22. A coated cemented carbide article as recited in claim 21 in
which said interlayer comprises a first layer of titanium carbide
disposed on said boron diffused surface region of said substrate
and a second layer of titanium nitride overlying said first layer
of titanium carbide.
23. A coated cemented carbide article as recited in claim 21 in
which said interlayer comprises a first layer of titanium carbide
disposed on said boron diffused surface region of said substrate;
and a second layer overlying said first layer of titanium carbide
said second layer being a mixture of titanium carbide and titanium
nitride.
Description
BACKGROUND OF THE INVENTION
The present invention relates to coatings on cemented carbide
bodies, and particularly, to the use of boride coatings on cemented
carbide substrates to obtain firm bonding and improve wear
resistance.
Cemented carbides are well known for their unique combination of
hardness, strength, and wear resistance, and are accordingly
extensively used for such industrial applications as cutting tools,
drawing dies and wear parts. For abrasive wear and nonferrous
metal-cutting applications, WC-Co compositions are preferred
because of their high strength and good abrasion resistance. For
steel machining applications, compositions consisting of
WC-TiC-TaC-Co, TiC-Ni or TiC-Ni-Mo are preferred because they are
less reactive with steel workpieces at high machining speeds. The
use of carbides other than WC generally results in a significant
strength reduction, however, which limits either the amount of TiC
and other carbides that can be added or the severity of the
application when large amounts of TiC are used.
The use of carbide, nitride, and carbonitride coatings on cemented
carbide is well known as a way to improve wear resistance in
machining and metal turning applications. However, it has been
found that such coatings do not possess the requisite hardness for
purely abrasive wear situations such as are encountered in the
drilling of rock and coal cutting. In addition, the carbide,
nitride, and carbonitride coated articles cannot be brazed to steel
holders because the liquid braze metal will not wet the carbide,
nitride, and carbonitride coatings.
The use of boride coatings represents an improvement over carbide,
nitride and carbonitride coatings. More particularly, boride
coatings, such as TiB.sub.2, are harder than carbide and nitride
coatings, such as TiC and TiN, and thus, more useful in purely
abrasive wear situations such as coal cutting and rock drilling. In
addition, boride coatings are easily wet by braze metals, and thus,
the boride coated articles can be brazed to steel holders. This
greatly facilitates their use in articles such as coal cutters and
roof support drilling tools which must be brazed.
THE PRIOR ART
Examples of the prior art include: U.S. Pat. No. 3,717,496 to
Kieffer, issued Feb. 20, 1973 and entitled "Machine Parts Having A
Wear And Abrasion Resistant Surface;" U.S. Pat. No. 2,844,492 to
Fitzer, issued July 22, 1958 and entitled "Method Of Producing Heat
Resisting Metallic Materials And Formed Bodies;" U.S. Pat. No.
3,029,162 to Samuel, issued Apr. 10, 1962 and entitled "Process For
The Production Of Metallic Borides On The Surface Of Metals;" U.S.
Pat. No. 3,661,524 to Holden, issued May 9, 1972 and entitled
"Preparation Of Titanium Carbide;" U.S. Pat. No. 3,712,798 to Van
Thyne, issued Jan. 23, 1973 and entitled "Chromium Boride Coated
Articles;" U.S. Pat. No. 3,787,245 to Kunst, issued Jan. 22, 1974
and entitled "Method For The Boration of Titanium And Titanium
Alloys;" U.S. Pat. No. 3,811,961 to Weinstein, issued May 21, 1974
and entitled "Boridized Steel-Bonded Carbides;" U.S. Pat. No.
3,836,392 to Lux et al, issued Sept. 17, 1974 and entitled "Process
For Increasing The Resistance To Wear Of The Surface Of Hard Metal
Cemented Carbide Parts Subject To Wear;" and U.S. Pat. No.
3,882,581 to Mereness et al, issued May 13, 1975 and entitled
"Coated, Partially Laminated Carbide Cutting Tool Insert."
Briefly, the Kieffer patent discloses the coating of a metallic
carbide substrate with a titanium compound to produce an abrasion
resistant surface by heating the substrate in the presence of
titanium tetrachloride and hydrogen peroxide. The Fitzer patent
broadly discloses the chemical vapor deposition of metallic boride
coatings by reaction of boron halides in a hydrogen carrier gas.
The Samuel patent relates to the coating of a metal substrate with
a metallic boride including titanium boride. The Holden patent
relates to the formation of a titanium carbide coating by reaction
with a titanium halide in a hydrogen atmosphere. The Van Thyne
patent relates to the coating of a substrate with a metallic
boride. The Kunst patent relates to the formation of titanium
boride. The Weinstein patent relates to the treatment of cemented
carbide surfaces with a boride coating. The Lux patent relates to
the coating of cemented carbide substrates. The Mereness patent
discloses a cemented carbide tool insert including a titanium
compound coating on the carbide substrate.
It is an object of the present invention to provide a new and
improved boride coated cemented carbide which exhibits a much
higher degree of wear resistance than the coatings of the prior
art.
It is another object of the subject invention to provide a new and
improved process for forming a boride coated cemented carbide.
SUMMARY OF THE INVENTION
The present invention relates to a new and improved boride coated
cemented carbide article, and a process which provides a
significant and surprising increase in the abrasion resistance of
known boride coated cemented carbide articles.
In the preferred embodiment of the present invention, the subject
coated cemented carbide article comprises a cemented carbide
substrate, the surface region of the substrate having been diffused
with an element such as boron, silicon or aluminum; an interlayer
disposed on the diffused substrate; and a boride coating disposed
on the interlayer. In accordance with the subject invention the
interlayer may comprise one or more layers each of which being
selected from the group consisting of the carbides, nitrides, and
carbonitrides of elements from groups IVb and Vb of the Periodic
Table of Elements and combinations thereof. The boride coating
disposed on the interlayer may be a boride such as titanium boride,
hafnium boride, zirconium boride or tantalum boride.
In another embodiment of the present invention the subject coated
cemented carbide comprises a cemented carbide substrate; an
interlayer disposed on the substrate; and a boride coating disposed
on the interlayer. Again, the interlayer may comprise one or more
layers each of which being selected from the group consisting of
the carbides, nitrides and carbonitrides, of elements from groups
IVb and Vb of the Periodic Table of Elements and Combinations
thereof. The boride coating disposed on the interlayer may be a
boride selected from the group consisting of titanium boride,
hafnium boride, zirconium boride, and tantalum boride.
In a further embodiment of the present invention, the subject
coated cemented carbide comprises a cemented carbide substrate, the
surface region of the substrate having been diffused with an
element such as boron, silicon or aluminum; and a boride coating
disposed on the diffused substrate, the boride coating being
selected from the group consisting of titanium boride, hafnium
boride, zirconium boride and tantalum boride.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention relates to new and improved boride coated
cemented carbide articles which may be formed into tools typically
used in machining applications, rock drilling, coal cutting, etc.
The invention also relates to a process which provides a
significant and very surprising increase in the abrasion resistance
of such boride coated cemented carbide articles. The term "cemented
carbide" as used herein means one or more transitional carbides of
a metal of Groups IVb and Vb and VIb of the Periodic Table of the
Elements, cemented or bonded by one or more matrix metals selected
from the Group Fe, Ni and Co. A typical cemented carbide may
contain WC in a cobalt matrix or TiC in a nickel matrix.
One of the problems faced in abrasive wear situations such as coal
cutting and rock drilling is to provide a hard coating which is
firmly bonded to a cemented carbide substrate and yet is brazeable
to steel holders. Boride coatings such as titanium boride
(TiB.sub.2) are harder than carbide and nitride coatings such as
TiC and TiN and thus the boride coatings has greater potential in
purely abrasive wear applications. It is an important requirement
that the boride coatings be firmly bonded to the cemented carbide
substrate in order to prevent loss of the coating of spalling. The
process disclosed herein achieves such firm bonding for abrasive
wear situations, and in addition, has a very surprising effect upon
the abrasion resistance of a cutting tool formed from the treated
carbide.
Turning first to the most preferred embodiment of the present
invention, the subject cemented carbide article comprises a
cemented carbide substrate, the surface region thereof having been
diffused with an element such as boron, silicon or aluminum; an
interlayer disposed on the diffused substrate; and a boride coating
disposed on the interlayer. In accordance with the subject
invention the diffusion depth may range from about 1 micron to
several hundred microns, such as for example up to 200 microns.
Preferably, however, the diffusion depth ranges from about 5 to 20
microns, with the optimum depth being about 15 microns. It has been
found that where the diffusion depth is in a range less than about
5 to 10 microns the wear resistance improvement of the article is
decreased, while in a range greater than about 20-30 microns the
toughness of the coated article decreases with little additional
improvement in the wear resistance.
The interlayer of the subject boride coated cemented carbide
article may be one or more layers each of which being selected from
the group consisting of the carbides, nitrides, and carbonitrides,
of elements from groups IVb and Vb of the Periodic Table of
Elements, and combinations thereof. The thickness of the
interlayers can vary from as low as a monoatomic layer to several
microns. The lower limit of interlayer thickness is determined by
the need to completely cover the substrate. The upper limit of
interlayer thickness is determined by the fact that as the
thickness of the interlayer increases a proportional loss of
strength and toughness is encountered. Accordingly, the upper limit
of interlayer thickness for practical purposes is about 10 microns.
The preferred interlayer thickness range is about 0.2 to 2.0
microns.
The boride coating disposed on the interlayer may be a boride such
as titanium boride, hafnium boride, zirconium boride or tantalum
boride. The thickness of the boride coating can broadly range from
about 1 to 20 microns. However, the wear resistance improvement
begins to decline where the boride coating thickness is less than
about 5 microns, and toughness is reduced where the boride coating
thickness is more than about 20 microns. In addition, there is
little additional increase in wear resistance when the boride
coating has a thickness greater than about 20 microns. Thus, for
practical purposes, it is preferable that the boride coating have a
thickness in the range of from about 5 microns to 20 microns, and
most preferably about 10 microns.
In order to more particularly point out the above-described
preferred embodiment of the subject invention reference is made to
the following Example.
EXAMPLE 1
A cemented carbide* rock drilling compact having 5/16inch diameter
hemispherical dome engagement surfaces was treated as follows:
(a) Heated to about 950.degree. C. and held for about ten minutes
in flowing H.sub.2 ;
(b) Exposed for about five minutes to H.sub.2 -1.5 volume %
BC1.sub.3 to deposit boron;
(c) Held for about twenty minutes at about 950.degree. C. in
flowing H.sub.2 to diffuse the boron for depth of about 15 microns
into the surface regions of the cemented carbide;
(d) Held for about twenty minutes at about 1050.degree. C. in a
flowing gas mixture of H.sub.2 -5 volume % CH.sub.4 -2 volume %
TiCl.sub.4 to deposit a layer of TiC about 11/2 microns thick onto
the boron diffused cemented carbide;
(e) Held for about fifteen minutes at about 1050.degree. C. in a
flowing gas mixture of H.sub.2 -33 volume % N.sub.2 -2 volume %
TiCl.sub.4 to deposit a layer of TiN about 11/2 microns thick
overlying the layer of TiC;
(f) Held for about ninety minutes at approximately 800.degree. C.
in a flowing gas mixture of H.sub.2 -3.3 volume % BCl.sub.3 -2
volume % TiCl.sub.4 to deposit TiB.sub.2 coating about 10 microns
thick. The above steps were conducted at a pressure of one
atmosphere.
______________________________________ *Chemical Composition (by
wt.) tungsten carbide, WC 84.0% cobalt, Co. 16.0% Hardness
(Rockwell A) 86.0-87.5 Density 13.9gm/cm.sup.3 Transverse Rupture
Strength 420,000 psi Ultimate Compressive Strength 560,000 psi
Ultimate Tensile Strength 270,000 psi Modulus of Elasticity 76
million psi Proportional Limit 100,000 psi Ductility (% elongation)
0.4% Impact Strength (Charpy) 25 in-lb ##STR1## 3 Electrical
Conductivity (%copper @ 25.degree. C.) 9.2% Electrical Resistivity
19.0 Microhm-cm ______________________________________ THERMAL
CONDUCTIVITY Cal TEMPERATURE .degree.C. (Sec.) (.degree.C.) (cm)
______________________________________ 50 0.21 100 0.19 150 0.19
200 0.19 250 0.19 300 0.19 400 0.19 500 0.19
______________________________________ COEFFICIENT OF THERMAL
EXPANSION From Room Temp. to .degree.F. Expansion per .degree.F.
.times. 10.sup.-6 ______________________________________ 400 3.2
750 3.3 1100 3.5 1500 3.8 1800 3.9
______________________________________
The compact thus prepared (X), along with an uncoated control
compact, were used to machine a block of sandstone rock 15 inches
long by 4 inches wide using a shaper machine. The cutting
conditions were a speed of 1200 inches per minute, a feed rate of
0.020 inches per pass, and depth of cut of 0.080 inches. Four cuts
across the rock were made. The results are shown in the following
table.
TABLE 1 ______________________________________ Weight Loss(gms)
Improvement Ratio ______________________________________ Uncoated
Control .2960 -- X .0069 43
______________________________________
Several other compacts were given treatments similar to that set
forth in Example 1 in order to determine acceptable ranges of the
various conditions applied. Accordingly, it has been found that
generally, the boron may be diffused into the substrate by passing
a mixture of hydrogen and about 0.1 to 5.0 volume percent of boron
trichloride gas over the substrate for about 5 to 60 minutes at
about 600.degree. C. to 1200.degree. C. The temperature ranges for
the deposition of the subject interlayers, (TiC and TiN in Example
1) are 700.degree. to 1300.degree. C. with the preferred range
being 900.degree. to 1100.degree. C. The accepted range of
pressures for the subject process is from about 5 torr. to one
atmosphere of pressure. The range of TiCl.sub.4 content in steps
(d), (e) and (f) is from about 1/2 volume % to 20 volume %. The
range of CH.sub.4 content in step (d) is 0 to about 20 volume %.
The range of N.sub.2 content in step (e) is from about 1 volume %
to 95 volume %. In addition to the above mentioned range of
TiCl.sub.4 content in step (f) the other conditions in step (f) are
a treatment time in the range of a few minutes to several hours, a
temperature range of from 600.degree. to 1200.degree. C., and a
BCl.sub.3 content in the range of about 1 to 5 volume %.
In another embodiment of the present invention the subject coated
cemented carbide article comprises a coated cemented carbide
substrate, the surface regions of the substrate having diffused
therein an element such as boron, silicon or aluminum; and a
coating disposed on the diffused substrate, the coating being a
boride such as titanium boride, hafnium boride, zirconium boride or
tantalum boride. The diffusion depth may range from about 1 micron
to several hundred microns, such as for example, 200 microns.
Preferably, however, the diffusion depth ranges from about 5 to 20
microns, with the optimum depth being about 15 microns. The
thickness of the boride coating can broadly range from about 1 to
20 microns. However, as indicated above relative to the first
embodiment of the present invention, for practical purposes it is
preferable that the boride coating have a thickness in the range of
from about 5 to 20 microns, and most preferably about 10
microns.
In order to more particularly point out this embodiment of the
present invention, reference is made to the following Example.
EXAMPLE 2
Cemented carbide rock drilling compacts, the same as in Example 1
above, were treated in the following manner:
(a) Heated to about 900.degree. C. and held for about fifteen
minutes in flowing H.sub.2 ;
(b) Held for about five minutes at 900.degree. C. in a flowing gas
mixture of H.sub.2 -7.9 volume % BCl.sub.3 to deposit boron
(c) Held for about twenty minutes at about 900.degree. C. in
flowing H.sub.2 to diffuse boron into the surface region of the
cemented carbide substrate;
(d) Held for about one hundred fifty minutes at about 800.degree.
C. in a flowing gas mixture of H.sub.2 -7.1 volume % BCl.sub.3 -2
volume % TiCl.sub.4 to deposit a TiB.sub.2 coating onto the boron
diffused substrate.
Compacts coated in this manner had TiB.sub.2 coatings ranging in
thickness from about 5 to 10 microns, and boron diffused into the
surface of the substrate to depths of from 5 to 20 microns. When
used to machine sandstone in the manner described in Example 1 the
treated compacts exhibited on improvement in wear resistance over
untreated, uncoated compacts in a range of about 5 to 50 times. It
will be noted that for comparison purposes, when rock drilling
compacts as in Example 1 were coated with TiB.sub.2 but without the
interlayers and diffusion of boron into the surface region of the
cemented carbide substrate as provided in Example 1, the wear
resistance obtained in the rock cutting test (the same as in
Example 1) was only a factor of 2 or 3 times better than the
uncoated, untreated compact. Additionally, when boron was diffused
into the cemented carbide substrate, but no coatings was deposited,
the wear resistance improvement was only a factor of about 2 to 3
over the untreated, uncoated compact. It will be further noted that
additional tests were conducted to determine acceptable ranges for
the various conditions in the subject process. Specifically, it was
found that generally, the boron may be diffused into the substrate
by passing a mixture of hydrogen and about 0.1 to 5.0 volume % of
boron trichloride gas over the substrate for about 5 to 60 minutes
at about 600.degree. C. to 1200.degree. C. The accepted range of
pressures for the subject process is from about 5 torr. to one
atmosphere of pressure. The range of conditions in step (f) are a
treatment in time in the range of a few minutes to several hours; a
temperature range of from 600.degree. to 1200.degree. C.; a
TiCL.sub.4 (step d) content of from about 1/2 volume % to about 20
volume %; and a BCl.sub.3 content in the range of about 1 to 5
volume % (steps b and d).
The additional tests indicated that when the element diffused into
the surface region of the cemented carbide substrate was boron, and
the cemented carbide was one having a cobalt matrix, where the
cobalt content was relatively low, i.e. on the order of 3 to 10
weight %, it was necessary to include a carbide, nitride or
carbonitride interlayer between the boron diffused substrate and
the titanium boride coating in order to obtain the preferred
adhesion of the titanium boride coating to the substrate. At higher
cobalt levels, however, i.e. on the order of 15 to 20 weight
percent, it was found that the interlayer was not necessary.
In a further embodiment of the present invention, the subject
coated cemented carbide article comprises, a cemented carbide
substrate; an interlayer disposed on the substrate; and a boride
coating disposed on the interlayer. In accordance with the subject
invention, the interlayer may comprise one or more layers each of
which being selected from the group consisting of the carbides,
nitrides, and carbonitrides of elements from groups IVb and Vb of
the Periodic Table of Elements, and combinations thereof. As in the
above described first embodiment of the present invention the
thickness of the interlayer can vary from as low as a monoatomic
layer to several microns, with the upper limit for practical
purposes being about 10 microns and the preferred range being about
0.2 to 2.0 microns.
The boride coating disposed on the interlayer may be a boride such
as titanium boride, hafnium boride, zirconium boride or tantalum
boride. The thickness of the boride coating can broadly range from
about 1 to 20 microns. However, the wear resistance improvement
begins to decline where the boride coating thickness is less than
about 5 microns, and toughness is reduced where the boride coating
thickness is more than about 20 microns. In addition, there is
little additional increase in wear resistance when the boride
coating has a thickness greater than about 20 microns. Thus, for
practical purposes, it is preferable that the boride coating have a
thickness in the range of from about 5 microns to 20 microns, and
most preferably about 10 microns.
In order to more particularly point out the above-described
preferred embodiment of the subject invention, reference is made to
the following Example.
EXAMPLE 3
Several cemented carbide* cutting inserts were treated in the
following manner:
(a) The inserts were heated to about 1050.degree. C. and held for
about fifteen minutes in an atmosphere of flowing hydrogen.
(b) They were then treated for about ten minutes at about
1050.degree. C. at a pressure of one atmosphere in an atmosphere of
H.sub.2, 2.5 volume % TiCl.sub.4 to form a thin (<1 micron)
adherent layer of TiC.
(c) They were then heated at about 800.degree. C., at a pressure of
one atmosphere for periods ranging from thirty minutes to ninety
minutes in an atmosphere of H.sub.2 -2.5 volume % TiCl.sub.4 -3
volume % BCl.sub.3 to obtain TiB.sub.2 coatings ranging in
thickness from about 2.3 to 7.5 microns.
______________________________________ *Chemical Composition (by
wt.) tungsten carbide, WC 94.0% cobalt, Co 6.0% Hardness (Rockwell
A) 91.7-92.2 Density 15.0 gm/cm.sup.3 Transverse Rupture Strength
290,000 psi Ultimate Compressive Strength 790,000 psi Ultimate
Tensile Strength 210,000 psi Modulus of Elasticity 94 million psi
Proportional Limit 280,000 psi Ducility (% elongation) 0.2% Impact
Strength (Charpy) 12 in-lb ##STR2## 35 Electrical Conductivity (%
copper @ 25.degree. C.) 10.2% Electrical Resistivity 17.0
Microhm-cm ______________________________________ THERMAL
CONDUCTIVITY Cal TEMPERATURE .degree. C. (Sec.)(.degree.C.)(cm)
______________________________________ 50 0.24 100 0.24 150 0.24
200 0.24 ______________________________________ COEFFICIENT OF
THERMAL EXPANSION From Room Temp. to .degree.F. Expansion per
.degree.F. .times. 10.sup.-6 ______________________________________
400 2.5 750 2.7 1100 2.8 1500 3.0 1800 3.0
______________________________________
These treated inserts were then used to machine a block of
sandstone rock 15 inches long by 4 inches wide using a shaper
machine. The cutting conditions were 1200 inches per minute speed,
0.050 inches per pass feed, and 0.040 inch depth of cut. Eight cuts
across the face of the sandstone block were made and the weight
loss of the cutting insert due to wear was measured as an
indication of wear resistance. An uncoated insert of the same
cemented carbide composition without an interlayer was subjected to
the same test for comparison purposes. The following table shows
the results obtained.
TABLE 2 ______________________________________ TiB.sub.2 Coating
Thickness Wt. Loss Improvement Run # (microns) (gms) Ratio
______________________________________ Control 0 .0145 -- A 4.5 (30
min. .0038 3.8 coating time) B 2.3 .0035 4.1 C 7.5 (90 min. .0022
6.6 coating time) ______________________________________
Additional tests were conducted to determine an acceptable range of
conditions for the subject process. Accordingly, it was found that
the range of temperatures for step (b) is about 700.degree. to
1300.degree. C., and preferably about 900.degree. to 1100.degree.
C. The acceptable range of pressures for steps (b) and (c) are from
about 5 torr. to one atmosphere. The TiCl.sub.4 content in steps
(b) and (c) is from about 1/2 volume % to about 20 volume %.
In summary, the present invention provides new and improved coated
cemented carbide articles which provide significant and very
surprising increases in the wear resistance of the articles.
Briefly, the present invention discloses three preferred
embodiments of coated cemented carbide articles. In one embodiment
the article comprises a cemented carbide substrate, the surface
regions of which having boron diffused therein; and a boride
coating disposed on the substrate. In another embodiment the
subject article further includes an interlayer sandwiched between
the boron diffused substrate and the boride coating, the interlayer
comprising one or more layers including the carbides, nitrides and
carbonitrides of elements of groups IVb and Vb of the Periodic
Table of Elements and combinations thereof. In a further
embodiment, the subject article includes a cemented carbide
substrate; an interlayer as described above, disposed on the
substrate; and a boride coating adhered to the interlayer. The
preferred process for treatment of cemented carbides in accordance
with the present invention is chemical vapor deposition. However,
other processes such as physical vapor deposition, pack diffusion
and coating, molten salt bath deposition, etc..., may also be
employed.
Whereas cemented carbide articles having boron diffused into the
substrate alone without a boride coating, or articles having a
boride coating on the substrate without any boron diffusion into
the substrate, exhibited in the above described tests a wear
resistance 2 to 3 times greater than untreated, uncoated articles,
the cemented carbide articles of the present invention exhibited a
very surprising increase in wear resistance over untreated,
uncoated articles, the improvement exhibited in said tests being on
the order of 20 to 50 times.
While there have been described herein what are at present
considered preferred embodiments of the invention, it will be
obvious to those skilled in the art that many modifications and
changes may be made therein without departing from the essence of
the invention. It is therefore to be understood that the exemplary
embodiments are illustrative and not restrictive of the invention,
the scope of which is defined in the appended claims, and that all
modifications that come within the meaning and range of equivalency
of the claims are intended to be included therein.
* * * * *